Supported catalysts containing a platinum group metal and method for producing diarylcarbonates

ABSTRACT

A platinum metal-containing supported catalyst in which the support contains mixed oxides of metals, transition metals and semiconductor elements, which can act as redox catalysts under the reaction conditions is disclosed. Also disclosed is the preparation of these catalysts and their use in a process for preparing diaryl carbonates.

This application is a 371 of PCT/EP98/04861 Aug. 5, 1998.

The present invention relates to platinum metal-containing supportedcatalysts in which the supports contain mixed oxides of metals,transition metals and semiconductor elements, which can act as redoxcatalysts under the reaction conditions and which have been prepared ina sol-gel process and use of the supported catalysts in a process forpreparing diaryl carbonates by reacting aromatic hydroxy compounds withcarbon monoxide and oxygen.

It is known that organic carbonates can be prepared by oxidativereaction of aromatic hydroxy compounds with carbon monoxide in thepresence of a noble metal catalyst (DE-OS 28 15 512). Palladium ispreferably used as the noble metal. In addition a co-catalyst (e.g.manganese or cobalt salts), a base, a quaternary salt, a variety ofquinones or hydroquinones and a drying agent may also be used. Theprocedure may be performed in a solvent, preferably in methylenechloride.

In order to perform this process in an economic manner, effectiverecovery of the noble metal catalyst is a critical factor, in additionto the activity and selectivity of the catalyst. On the one hand thenoble metal catalyst represents a large cost factor. Losses of noblemetal catalyst have to be replaced at great cost. On the other hand noresidues of the noble metal catalyst should remain in the product. Theeconomic and efficient recovery of homogeneous catalysts for the processof oxidative carbonylation of aromatic hydroxy compounds to give diarylcarbonates has not hitherto been described. The separation of a noblemetal catalyst from a liquid reaction mixture, e.g. by filtering orcentrifuging, can be performed at low cost if heterogeneous supportedcatalysts are used.

In EP-A 572 980, EP-A 503 581 and EP-A 614 876 noble metal supportedcatalysts are used which contain 5% palladium on carbon supports.However, these types of supported catalysts produce only veryunsatisfactory conversions or even none at all, so that these are alsounsuitable for an economically viable process.

JP-A 01/165 551 (cited in accordance with C.A. 112:76618j (1990))describes using palladium or palladium compounds such as palladiumacetylacetonate, in combination with alkali metal or alkaline earthmetal iodides or ‘onium’ iodides, such as tetrabutylammonium iodide, andat least one zeolite to prepare aromatic carbonates.

JP-A 04/257 546 and JP-A 04/261 142 each describe an example of asupported catalyst for preparing aromatic carbonates in which siliconcarbide granules are used as the support material for a supportedcatalyst in a distillation column. Although drastic conditions (highpressure, high temperature) are used in the relevant examples, thesecatalysts produce only very low space-time yields. These low space-timeyields make the economic production of aromatic carbonates with thistype of supported catalyst impossible.

EP-A 736 324 describes the preparation of diaryl carbonates withheterogeneous catalysts which contain a platinum metal, preferablypalladium, and a co-catalytic metal compound, preferably a metal fromthe group Mn, Cu, Co, Ce and Mo. When preparing the catalysts theco-catalytic metals are applied to a support.

EP-A 736 325 describes the preparation of diaryl carbonates withheterogeneous catalysts which contain a platinum metal, preferablypalladium, on a support which consists of a metal oxide in which themetal may exist in several valency states.

Although these supported catalysts enable the preparation of aromaticcarbonates for the first time, a further increase in activity isdesirable from an economic point of view.

It has now been found that higher catalyst activities can be obtained ifplatinum metal-containing supported catalysts in which the supportcontains mixed oxides e.g. of V, Mn, Ti, Cu, La, the rare-earth metalsand mixtures thereof which act as redox catalysts under the reactionconditions, which have been prepared in a sol-gel process and whichcontain platinum metals are used as catalysts.

The invention provides catalysts which contain

(i) an oxide of the elements silicon, aluminium, titanium, zirconium ora mixture of oxides of these elements,

(ii) one or more co-catalytic metal oxides from groups 4, 5, 6, 7, 11,12, 13, 14, the iron group (atomic numbers 26 to 28) or the rare-earthmetals (atomic numbers 58 to 71) in the periodic system of the elementsin accordance with the new IUPAC nomenclature, and

(iii) one or more platinum metals or one or more compounds of platinummetals (atomic numbers 44 to 46 and 77 and 78) in an amount 0.01 to 15wt. %, calculated as platinum metal and with respect to the total weightof catalyst,

which are obtained by preparing a gel from one or more suitableprecursor(s) of the components mentioned under (i) and (ii), ageing,drying and optionally annealing the gel, shaping the mixed metal oxideobtained in this way and then applying the platinum metal component(iii) to the mixed metal oxide.

Supports according to the invention probably act like a separately addedco-catalyst, but they avoid all disadvantages of separately addedco-catalysts such as mixing with the reaction product and thuscontaminating it. In accordance with this hypothesis, all the metalsmentioned are those which can occur in several valency states. As aresult of the special method of preparation, mixed oxides according tothe invention are obtained which produce particularly active catalystsas compared with the prior art. This is particularly surprising sincethe activity of known catalysts is only very slightly affected by themethod of preparation of the support.

Catalysts according to the invention contain, when ready to react

(i) an oxide of the elements silicon, aluminium, titanium, zirconium ora mixture of oxides of these elements,

(ii) one or more co-catalytic metal oxides of the groups 4, 5, 6, 7, 11,12, 13, 14, the iron group (atomic numbers 26 to 28) or the rare-earthmetals (atomic numbers 58 to 71) in the periodic system of the elements(IUPAC, new), and

(iii) one or more platinum metals or one or more compounds of platinummetals (atomic numbers 44 to 46 and 77 and 78) in an amount 0.01 to 15wt. %, preferably 0.05 to 10 wt. %, calculated as platinum metal andwith respect to the total weight of catalyst.

Catalysts according to the invention are prepared by preparing a gelfrom one or more suitable precursor(s) of the components mentioned under(i) and one or more suitable precursor(s) of the components mentionedunder (ii), ageing the gel, drying and optionally annealing the gel,making the mixed metal oxide obtained into the desired form, e.g.powder, granules, extrudate, spheres, cylinders, hollow rings, usingmethods known to a person skilled in the art, and then applying theplatinum metal components to the catalyst supports being used accordingto the invention using methods basically known to a person skilled inthe art, such as, for example, soaking, adsorption, immersion, spraying,impregnation and ion exchange.

The mixed metal oxide supports are used according to the invention aspowders, tablets or binder-containing extrudates. Suitable binders aree.g. SiO₂, Al₂O₃ or aluminas. The concentration of binder may be variedover a wide range, for example 0.5 to 99.5 wt. %, with respect to thetotal weight of support. The mixed metal oxide may also be applied as alayer on an inert material (wash coat).

The gel according to the invention can be prepared by almost any knownmethod. Methods which are known for preparing mixed oxides based on agel are preferably used. This includes, for example, the hydrolysis ofone or more metal alkoxides and/or hydrolysable metal compounds underacid, neutral or basic conditions in suitable solvents at temperaturesof 0° C. to 200° C. In this case mixtures of different precursors of oneor more elements may also be used.

Suitable precursors of silicon dioxide are alkoxides of silicon such as,for example, tetraethoxysilane, tetramethoxysilane.

Suitable precursors of aluminium oxide are lower alkoxides such astrimethoxyaluminium, triethoxyaluminium, tri-n-propoxyaluminium,tri-iso-propoxyaluminium, tri-sec-butoxyaluminium,tri-sec-butoxyaluminium, or tri-tertbutoxyaluminium or aluminiumalkoxides with chelating ligands such asdibutoxyaluminium-ethylacetoacetate.

Suitable precursors of titanium oxide are tetramethoxytitanium,tetraethoxytitanium, tetraisopropoxytitanium; suitable precursors ofzirconium oxide are tetraethoxyzirconium, tetra-tert-butoxyzirconium,tetra-n-butoxyzirconium, tetra-isopropoxyzirconium. Suitablehydrolysable salts are for example titanium tetrachloride, organic saltssuch as aluminium acetylacetonate, zirconium acetylacetonate or thecorresponding mixed metal compounds and salts.

Suitable solvents are, for example, monohydric alcohols such asmethanol, ethanol, n-propanol, iso-propanol, n-butanol, 2-butanol,t-butanol, polyhydric alcohols such as glycol, 1,2-propanediol,1,3-propanediol, monofunctional or polyfunctional ketones such asacetone, 1,3-pentanedione (acetylacetone), cyclic or linear ethers withone to three oxygen atoms such as tetrahydrofuran, dioxan, diethylether, glycoldiethyl ether or diethyleneglycoldiethyl ether,ether-alcohols such as glycolmonomethyl ether, nitriles such asacetonitrile and benzonitrile and amides such as dimethylformamide.Alcohols, diketones and ether-alcohols are preferred. Obviously mixturesof solvents may also be used.

The solvents are used in amounts such that the molar ratio of alkoxideto solvent is 1:0.2 to 1:100.

Partially alkylated precursors R¹ _(x)(OR²)_(y) may also be used in theprocess according to the invention, wherein M represents one of theelements mentioned under (i), (x+y) is the valency of the element and R¹and R², independently of each other, represent alkyl, aralkyl or arylgroups with 1 to 20 carbon atoms. The following may be mentioned by wayof example: methyltriethoxysilane, ethyltriethoxysilane.

Co-catalytic compounds which may be mentioned are one or more compoundsof elements from the groups 4, 5, 6, 7, 11, 12, 13, 14, the iron group(atomic numbers 26 to 28) or the rare-earth metals (atomic numbers 58 to71) in the periodic system of elements (IUPAC, new) with a total molarproportion of the components mentioned under (ii) of 0.1% to 99.9%,preferably 0.1% to 40%, in particular 0.5% to 20%, with respect to thetotal number of moles of the components mentioned under (i) and (ii),introduced into the catalyst, preferably Mn, Cu, Co, V, Nb, W, Zn, Ce,Mo, in particular Mn, Co, Cu, Mo, Ce, quite specifically Mn and/or Ce.

Suitable precursors of the co-catalytic metals are basically known, andthe following may be used for example: inorganic salts such as halides,oxides, nitrates, sulphates, carboxylates, salts of monofunctional orpolyfunctional organic C₂ to C₁₅ carboxylic acids such as acetates,cyclohexane butyrates, diketonates such as acetylacetonate, ethylhexanoate, alkoxides such as methoxides, ethoxides and isopropoxides andcomplex compounds which contain, for example, carbon monoxide, olefins,amines, nitriles, phosphines and halides, as well as mixed salts.

Heterometallic alkoxides of the formula [L_(m)—(OR)₂—M′L_(n)′] are alsoknown and are described, for example, by Mehrotra et al in Mat. Res.Soc. Symp. Proc. 121 (1988) 81; D. C. Bradley et al in “MetalAlkoxides”, Academic Press, NY (1978); K. G. Caulton et al in Chem. Rev.90 (1990) 969.

Examples of compounds containing organic ligands which may be mentionedare: cerium (IV) isopropoxide, cerium (IV) methoxyethoxide, cerium (III)acetylacetonate, cobalt carbonylmethoxide, cobalt (II) acetylacetonate,cobalt (III) acetylacetonate, manganese (II) ethoxide, manganese (II)acetylacetonate, manganese (III) acetylacetonate, copper (II)2-ethylhexanoate, copper (II) ethoxide, copper (II) ethylacetoacetate,copper (II) acetylacetonate niobium (V) ethoxide, molybdenum (V)ethoxide (dimolybdenum decaethoxide), molybdenum (VI)oxide-bisacetylacetonate, vanadium (IV) oxide-bisacetylacetonate(vanadyl acetylacetonate), vanadium (III) acetylacetonate, vanadiumtriisopropoxide oxide, vanadium tri-n-propoxide oxide, tungsten (VI)ethoxide, tungsten (V) ethoxide, tungsten (VI) phenoxide, zinc (II)acetylacetonate.

Suitable platinum metal compounds are, for example, the platinum metalcompounds and platinum metal-containing complex compounds described inEP-A 736 324. In the examples mentioned, palladium was mentioned as theplatinum metal, but other platinum metals are also suitable such as Pt,Ir, Ru or Rh. Pd and Rh, however, are preferred, in particular Pd.

Catalysts according to the invention are prepared in at least two steps.A mixed metal oxide which does not contain any platinum metal isinitially prepared using the method described above, optionally madeinto the required form and then the platinum metal is applied to themixed metal oxide by methods known to a person skilled in the art.

When preparing catalysts according to the invention, a solution of theprecursors of (i) and (ii) are conventionally prepared in a suitablesolvent and hydrolysed with 1 to 20, preferably 1.5 to 10 moleequivalents of water, with respect to the total number of moles ofcompounds (i) and (ii). The water may be added in one or severalportions, pure, mixed with other solvents or together with precursors of(ii) dissolved therein.

During the hydrolysis procedure, acids or bases may be added in amountsof 0.1 to 200 mol. % with respect to the total number of moles ofcompounds (i) and (ii).

Suitable acids are, for example, hydrochloric acid, nitric acid,sulphuric acid, formic acid, acetic acid or higher carboxylic acids with3 to 8 carbon atoms. Di- and tricarboxylic acids with up to 8 carbonatoms are also suitable. Suitable bases are ammonia, quaternary ammoniumhydroxides, NR₄OH, in which the R groups, independently of each other,may be alkyl, aryl or aralkyl groups with 1 to 15 carbon atoms, e.g.tetramethyl-, tetraethyl-, tetrapropyl-, tetrabutyl-, tetrapentyl- ortetraphenylammonium hydroxide, or organic nitrogen bases such as amines,pyridines, guanidines. Preferred bases are ammonia and quaternaryammonium hydroxides. The acids and bases may be used as pure substances,as anhydrous solutions or as aqueous solutions.

When adding the individual components, efficient homogenisation of themixture should be ensured by using appropriate mixing devices such ase.g. stirrers or mixing nozzles.

If several compounds (i) and (ii) are hydrolysed, known techniques maybe applied in order to mutually adjust their reactivities. The followingmay be mentioned by way of example: pre-hydrolysis of one compound,chemical modification of one compound with a chelating agent, the use ofdifferent alkoxide groups in the compounds and hydrolysis at differenttemperatures, such as is described, for example, by D. A.Ward and E.I.Ko (Ind. Eng. Chem. Res. 34 (1995) 421).

Another suitable method for preparing mixtures according to theinvention from precursors of (i) and (ii) is the gelling of inorganicprecursors in aqueous systems, such as the preparation of silica gels byneutralising alkali metal silicates with strong acids. Additional steps,such as washing the gel, may be required in order to wash salts whichhave been formed out of the mixture. During the procedure described herethe precursor of (ii) may be added, for example, to one of thecomponents before mixing the alkali metal silicate and acid.

After gelling, it is advantageous to allow the gels to age attemperatures of 20 to 100° C., preferably 20 to 80° C., for a period ofat least 10 minutes. The upper limit to the ageing time is restrictedonly by economic factors and may be several weeks. Times between onehour and two weeks are preferred. Ageing may also be performed inseveral steps at different temperatures or at a temperature whichchanges slowly with time.

The gels are dried after they have been aged. Drying the gels may beperformed by a variety of methods, depending on the method ofpreparation, wherein drying has an effect on the internal surface areaand the pore volume of the materials.

Drying may take place on the one hand in air, under a vacuum or in astream of gas. Suitable gases for drying the gel in a gas stream arenitrogen, oxygen, carbon dioxide or noble gases or any mixture of thegases mentioned, preferably e.g. air. Gaseous hydrocarbons for examplealkanes such as methane, ethane, propane, butane, alkenes such asethene, propene, butene, butadiene and alkynes such as ethyne, propyne,etc in any composition may also be used. Drying is performed at 0 to300° C., preferably 20 to 250° C., in particular at 20 to 150° C. Thedrying time depends e.g. on the porosity of the gel and on the solventused. It is generally a few hours, for example 0.5 to 50 h, preferably 1to 40 h, in particular 1 to 30 h.

Another preferred method is drying under supercritical conditions suchas, for example, is described by G. M. Pajonk (Applied Catalysis 72(1991) 217) and Dutoit et al (J. Catal. 161 (1996) 651), and this leadsto gels with particularly high porosities. Carbon dioxide(T_(critical)=31° C., P_(critical)=73 bar) or alcohols above theircritical point (e.g. for ethanol T_(critical)=243° C., P_(critical)=63bar), for example, may be used. Drying may be performed, batchwise,continuously or part-continuously, optionally in the presence of anotherinert gas.

Reduction of the platinum metal may occasionally occur duringsupercritical drying with alcohols and this generally has a negativeeffect on the activity of the catalysts according to the invention. Inthese cases it is recommended that the catalysts be oxidised again afterdrying, for example by annealing at 200 to 800° C. in a stream of gaswhich contains oxygen, air, halogens or hydrogen halides.

Further methods of drying, particularly for gels prepared in aqueoussystems, are extractive and azeotropic drying such as are described, forexample, in U.S. Pat. No. 3,887,494, US-A 3,900,457, US-A 4,169,926,US-A 4,152,503, US-A 4,436,883 or US-A 4,081,407.

After drying the dried mixed oxides may be calcined. This may takeplace, in the case of mixed oxides prepared in several steps, eitherbefore or after applying the platinum metal, or several times. Calciningmay take place in air, under vacuum or in a gas stream. Suitable gasesfor calcining mixed oxides in a gas stream are e.g. nitrogen, oxygen,carbon dioxide or noble gases and any mixtures of the gases mentioned,preferably air. Calcining is performed at 100 to 800° C., preferably at100 to 700° C., in particular at 100 to 600° C. It may sometimes be ofadvantage if the composition of the gas is altered either suddenly orcontinuously during calcination. The calcining time is generally a fewhours, for example 0.5 to 50 h, preferably 1 to 40 h, in particular 1 to30h.

In a preferred variant of the method of preparing the catalyst, theplatinum metal is applied to the previously-prepared metal mixed oxide.Methods may be used for this which are basically known to a personskilled in the art and are described, for example, in EP-A 736 325. Themixture may be stirred during application of the platinum metal to themetal mixed oxide. However, it may also be advantageous to allow themixture to stand or to shake it.

After applying platinum metal to the support, the supported catalyst isisolated, e.g. by filtering, sedimentation or centrifuging. In a furtherembodiment of the invention the solvent is separated by distillation.

After separating the solvent, the supported catalysts obtained in thisway are dried. The drying procedure is preferably performed in air,under vacuum, or in a gas stream under the conditions given above fordrying the gels. A calcination step may be performed under theconditions described above, after the drying procedure.

It is also possible to apply the mixed oxides according to the inventionas a layer on other catalyst supports. Suitable support materials forthe application of a layer of metal mixed oxide are any industriallyconventional catalyst supports based on carbon, oxides of elements,carbides of elements or salts of elements in a variety of forms.Examples of carbon-containing supports are coke, graphite, carbon blackor active carbon. Examples of elemental oxide catalyst supports are SiO₂(natural or synthetic silicas, quartz), Al₂O₃ in a variety ofmodifications (α, γ, δ, η, θ), aluminas, natural and syntheticaluminosilicates (zeolites), TiO₂ (rutile, anatase), ZrO₂ or ZnO.Examples of elemental carbides and salts are SiC, AlPO₄, BaSO₄, CaCO₃,etc. They may be used either as chemically uniform pure substances or asmixtures. Particulate or powdered materials, or even monoliths, aresuitable for use according to the invention. Particulate materials areparticularly preferred.

The invention also provides a process for preparing an organic carbonateby reacting an aromatic hydroxy compound with carbon monoxide and oxygenin the presence of the catalysts according to the invention, aquaternary ammonium or phosphonium salt and a base.

The organic carbonate prepared by the process according to the inventioncorresponds to the formula

R—O—CO—O—R  (I)

in which

R represents a substituted or non-substituted C₆-C₁₂ aryl group,preferably a substituted or non-substituted phenyl group, in particulara non-substituted phenyl group.

Aromatic hydroxy compounds which may be used according to the inventioncorrespond to the formula

R—O—H  (II)

in which R is defined as above. Aromatic hydroxy compounds which can bereacted using the supported catalysts according to the invention are forexample phenol, o-, m- or p-cresol, o-, m- or p-chlorophenol, o-, m- orp-ethylphenol, o-, m- or p-propylphenol, o-, m- or p-methoxyphenol,2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol,2-naphthol or bisphenol-A, preferably phenol. The aromatic hydroxycompound may be substituted with one or two substituents such as a C₁-C₄alkyl group, a C₁-C₄ alkoxy group, fluorine, chlorine or bromine.

Catalysts according to the invention may be used as powders, mouldeditems or monoliths, preferably as powders or moulded items, and areseparated from the reaction mixture by e.g. filtration, sedimentation orcentrifuging.

Preparation of aromatic carbonates using supported catalysts accordingto the invention may be performed in a variety of ways. One possibilityis a batchwise process. In the event of a continuous mode of operationin either a counter-flow or parallel flow system, or in the tricklephase on a fixed bed catalyst, loads of 0.01 to 20 g of aromatic hydroxycompound per gram of supported catalyst per hour, preferably 0.05 to 10g of aromatic hydroxy compound per gram of supported catalyst per hour,in particular 0.1 to 5 g of aromatic hydroxy compound per gram ofsupported catalyst per hour are used. The supported catalyst used inbatchwise trials may be used repeatedly with the same feed materialswithout any purification. With a continuous mode of operation thesupported catalysts used may remain in the reactor for a long time. Acontinuous mode of operation in a single reactor or in a cascade ofreactors are preferably used when using supported catalysts according tothe invention.

If the supported catalyst is used as a powder, the stirred container tobe used for mixing the reaction components is fitted with stirrers whichcan be used for this purpose. When working with supported catalystpowders as a suspension in stirred vessels or bubble columns, amounts of0.001 to 50 wt. %, preferably 0.01 to 20 wt. %, in particular 0.1 to 10wt. % of supported catalyst powder, with respect to the amount ofaromatic hydroxy compound used, are used. In particularly preferredembodiments, the heterogeneous supported catalyst is used as mouldeditems fixed in place in stirred tanks, bubble columns, trickle phasereactors or cascades of these reactors, wherein different types ofreactors may also be used in combination in a cascade.

In the event that the catalyst is arranged as a fixed bed, the catalystis preferably used as moulded items, e.g. as spheres, cylinders, smallrods, hollow cylinders, rings, etc. If required, catalysts may bemodified further by extruding, making tablets, optionally adding furthercatalyst supports or binders such as SiO₂ or Al₂O₃, and calcining. Thepreparation and further processing of catalysts used according to theinvention are generally known to a person skilled in the art and arepart of the prior art.

In the process according to the invention any organic or inorganic basesor mixtures of these may be used. Examples of inorganic bases which maybe mentioned, without restricting the process according to theinvention, are alkali metal hydroxides and carbonates, carboxylates orother salts of weak acids and alkali metal salts of aromatic hydroxycompounds of the formula (II), e.g. alkali metal phenolates. Obviouslythe hydrates of alkali metal phenolates may also be used in the processaccording to the invention. An example of this type of hydrate which maybe mentioned here, without restricting the process according to theinvention, is sodium phenolate trihydrate. The amount of added water,however, is preferably such that a maximum of 5 moles of water are usedper mole of base. Higher amounts of water lead, inter alia, to poorerconversions and decomposition of the carbonates being formed. Examplesof organic bases which may be mentioned, without restricting the processaccording to the invention, are tertiary amines which may have C₆-C₁₀aryl, C₇-C₁₂ aralkyl and/or C₁-C₂₀ alkyl groups as organic groups, orpyridine bases or hydrogenated pyridine bases, for exampletriethylamine, tripropylamine, tributylamine, trioctylamine,benzyldimethylamine, dioctylbenzylamine, dimethylphenethylamine,1-dimethylamino-2-phenylpropane, pyridine, N-methylpiperidine,1,2,2,6,6,-pentamethylpiperidine. An alkali metal salt of an aromatichydroxy compound is preferably used as the base, in particular an alkalimetal salt of the aromatic hydroxy compound which is also being reactedto give the organic carbonate. This alkali metal salt may be a lithium,sodium, potassium, rubidium or caesium salt. Lithium, sodium andpotassium phenolate are preferably used, in particular sodium phenolate.

The base may be added to the reaction mixture as the pure compound insolid form or as molten material. In a further embodiment of theinvention the base is added to the reaction mixture as a solution whichcontains 0.1 to 80 wt. %, preferably 0.5 to 65 reaction mixture as asolution which contains 0.1 to 80 wt. %, preferably 0.5 to 65 wt. %, inparticular 1 to 50 wt. % of the base. Solvents which may be used forthis are either alcohols or phenols such as e.g. the phenolparticipating in the reaction or also inert solvents. Examples are thosementioned below for use as reaction media. These solvents may be usedindividually or in any combination with each other. Thus there is oneembodiment of the process according to the invention, for example, inwhich the base is dissolved in a molten phenol which has been dilutedwith a solvent. The base is preferably dissolved in a molten aromatichydroxy compound, in particular in the molten aromatic hydroxy compoundwhich is intended to be reacted to give the organic carbonate. Quitespecifically the base is dissolved in phenol. The base is added in anamount which does not depend on the stoicheiometry. The ratio ofplatinum metal, e.g. palladium, to base is preferably chosen so that 0.1to 500, preferably 0.3 to 200, in particular 0.9 to 130 equivalents ofbase, with respect to platinum metal, e.g. palladium, are used per moleof platinum metal, e.g. palladium.

The process according to the invention is preferably performed withoutusing a solvent. Obviously inert solvents may also be used. Examples ofsolvents which may be mentioned are dimethylacetamide,N-methylpyrrolidinone, dioxan, t-butanol, cumyl alcohol, isoamylalcohol, tetramethylurea, diethyleneglycol, halogenated hydrocarbons(e.g. chlorobenzene or dichlorobenzene) and ethers.

The quaternary salts used in the context of the present invention maybe, for example, ammonium or phosphonium salts substituted with organicgroups. Compounds suitable for use in the process according to theinvention are ammonium and phosphonium salts which contain, as organicgroups, C₆-C₁₀ aryl, C₇-C₁₂ aralkyl and/or C₁-C₂₀ alkyl groups and, asanion, a halide, tetrafluoroborate or hexafluorophosphate. Ammoniumsalts which are preferably used in the process according to theinvention contain, as organic groups, C₆-C₁₀ aryl, C₇-C₁₂ aralkyl and/orC₁-C₂₀ alkyl groups and, as anion, a halide, in particulartetrabutylammonium bromide. The amount of this type of quaternary saltis 0.1 to 50 wt. %, with respect to the weight of the reaction mixture.This amount is preferably 0.5 to 15 wt. %, in particular 1 to 5 wt. %.

The process according to the invention, preferably without a solvent, isperformed at 30 to 200° C., preferably 30 to 150° C., in particular 40to 120° C. at a pressure of 1 to 100 bar, preferably 2 to 50 bar, inparticular 5 to 25 bar.

EXAMPLES Comparison Example 1

(In Accordance with EP-A 736 324)

Preparing a Powdered Manganese Oxide Support:

85 g of sodium hydroxide (2.125 mol) dissolved in 200 ml of water wereadded dropwise to a solution of 126 g of manganese (II) chloride (1 mol)in 500 ml of water. The precipitate obtained in this way was filteredunder suction, washed and dried. Then it was annealed for 3 h at 300° C.and for 2 h at 500° C.

Coating the Powdered Manganese Oxide with Palladium:

300 ml of a solution of 50 g of sodium tetrachloropalladate (II) hydratecontaining 15 % palladium in water were added to a slurry of 292.5 g ofmanganese dioxide powder in 1500 ml of water at room temperature. Themixture was adjusted to be alkaline using dilute caustic soda. Thesuspension was filtered under suction and dried at 100° C. Theheterogeneous catalyst contained 2.5% palladium on an MnO₂ support,calculated as metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate:

8.31 g of tetrabutylammonium bromide and 0.77 g of manganese (II)acetylacetonate dissolved in 450 g of phenol were introduced into anautoclave (1 litre) with a gas dispersion stirrer and condenser and witha cold trap connected in series. Then 4 g of the supported catalystdescribed above and 2.21 g of sodium phenolate dissolved in 50 g ofphenol were added. The pressure was then adjusted to 14 bars byintroducing a gaseous mixture of carbon monoxide and oxygen (95:5 vol.%). The amount of gaseous mixture was adjusted to 350 Nl/h. A sample waswithdrawn from the reaction mixture each hour and analysed gaschromatographically. The analyses showed that after 1 h 9.9% of diphenylcarbonate, after 2 h 15.2% of diphenyl carbonate and after 3 h 18.2 % ofdiphenyl carbonate were present in the reaction mixture. 11.8 g of aphenol/water mixture had condensed in the cold trap.

Comparison Example 2

(In Accordance with EP-A 736 325)

Coating a Powdered Titanium Dioxide with Palladium and Manganese:

300 ml of a solution of 40.5 g (0.16 mol) of manganese (II) nitratetetrahydrate in water were added to a slurry of 283.5 g of titaniumdioxide powder (Norton) in 1500 ml of water at room temperature. Themixture was then made alkaline with dilute caustic soda solution. Thesuspension was filtered under suction, washed with water, dried at 100°C. and annealed for 3 h at 300° C. The support, doped with manganese,was slurried in 1500 ml of water and then 300 ml of solution containing50 g of sodium tetrachloropalladate (II) hydrate containing 15% ofpalladium were added. The mixture was adjusted to be alkaline withdilute caustic soda solution. The suspension was filtered under suction,washed and dried at 100° C.

The catalyst contained 2.5% palladium and 3% manganese, each calculatedas the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate:

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in comparison example 1. The analyses showed thatafter 1 h 9.6% of diphenyl carbonate, after 2 h 16.1% diphenyl carbonateand after 3 h 21.0% diphenyl carbonate were present in the reactionmixture. 12.3 g of phenol/water mixture had condensed in the cold trap.

Example 1

Preparing a Si/Mn co-gel and Coating with Palladium

5.2 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. 36 mlof 8N HCl were added to the mixture with stirring over the course of 18minutes. The mixture was covered loosely with paper and allowed to standfor 6 days at room temperature to gel. Then the gel was dried for 2 daysat 40° C. in a vacuum drying cabinet, milled to give a powder and thepowder was annealed for 3 h at 300° C. in air.

0.54 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 0.7% palladium and 3% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The trial was performed in the same way as described in comparisonexample 1, but with the difference that 14.3 g of catalyst were used.Analysis showed that after 1 h 12 % diphenyl carbonate, after 2 h 17.6%diphenyl carbonate and after 3 h 24.1% diphenyl carbonate were presentin the reaction mixture. 14.1 g of a phenol/water mixture had condensedin the cold trap.

Example 2

Preparing a Si/Mn co-gel and Coating with Palladium

5.2 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. 36 mlof 8N HCl were added to the mixture with stirring over the course of 18minutes. The mixture was covered loosely with paper and allowed to standfor 3 weeks at room temperature to gel. Then the gel was dried for 2days at 40° C. in a vacuum drying cabinet, milled to give a powder andthe powder was annealed for 3 h at 300° C. in air.

0.54 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 0.7% palladium and 3% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 1. Analysis showed that after 1 h 14.0% diphenylcarbonate, after 2 h 20.6% diphenyl carbonate and after 3 h 26.7%diphenyl carbonate were present in the reaction mixture. 16.7 g of aphenol/water mixture had condensed in the cold trap.

Example 3

Preparing a Si/Mn co-gel and Coating with Palladium

10.4 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. 36 mlof 8N HCl were added to the mixture with stirring over the course of 18minutes. The mixture was covered loosely with paper and allowed to standfor 6 days at room temperature to gel. Then the gel was dried for 2 daysat 40° C. in a vacuum drying cabinet, milled to give a powder and thepowder was annealed for 3 h at 300° C. in air.

1.76 g of sodium tetrachloropalladate trihydrate were dissolved in 100 gof water, the dried and powdered gel was added thereto and stirred for 2h at 60° C. on a Rotavapor. The solvent was then distilled off and thecatalyst dried overnight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 2.0% palladium and 6% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 2, with the difference that 5.0 g of catalystwere used. Analysis showed that after 1 h 16.4% diphenyl carbonate,after 2 h 22.0% diphenyl carbonate and after 3 h 27.2% diphenylcarbonate were present in the reaction mixture. 12.1 g of a phenol/watermixture had condensed in the cold trap.

Example 4

Preparing a Si/Mn co-gel and Coating with Palladium

10.4 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. Asolution of 1.8 g of glacial acetic acid in 27 g of distilled water wasadded to the mixture with stirring. The mixture was covered loosely withpaper and allowed to stand for 10 days at room temperature to gel. Thenthe gel was dried for 2 days at 40° C. in a vacuum drying cabinet,milled to give a powder and the powder was annealed for 3 h at 300° C.in air.

0.77 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 1.0% palladium and 6% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 3, with the difference that 10.0 g of catalystwere used. Analysis showed that after 1 h 11.9% diphenyl carbonate,after 2 h 18.3% diphenyl carbonate and after 3 h 24.3% diphenylcarbonate were present in the reaction mixture. 12.1 g of a phenol/watermixture had condensed in the cold trap.

Example 5

Preparing a Al/Mn co-gel and Coating with Palladium

50 g of aluminium sec-butylate were mixed with 200 ml of 2-butanol and asolution of 6.6 g Mn(acac)₃ in 100 ml of warm acetone was added thereto.The mixture was heated to 40° C. and a mixture of 10 ml of distilledwater in 100 ml of methanol was added slowly with stirring on aRotavapor. After one hour the mixture was heated to 60° C. and stirredfor 20 h at this temperature. The solvent was distilled off, the residuedried overnight at 110° C. in a vacuum drying cabinet, and then driedfor 3 h at 350° C. in a stream of air.

0.42 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 0.7% palladium and 5% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 2. Analysis showed that after 1 h 11.9% diphenylcarbonate, after 2 h 17.6% diphenyl carbonate and after 3 h 23.7%diphenyl carbonate were present in the reaction mixture. 13.5 g of aphenol/water mixture had condensed in the cold trap.

Example 6

Preparing a Zr/Mn co-gel and Coating with Palladium

12.1 g of Mn(acac)₃ were dissolved in 600 ml of ethanol in apolypropylene beaker and under a nitrogen atmosphere and then 143 g of a70% strength solution of zirconium n-propoxide were added. A mixture of12 ml of distilled water and 13 g 8N HCl (25.7 wt. %) were added slowlyto the mixture with stirring. The mixture was covered loosely with paperand allowed to stand for 7 days at room temperature to gel. Then the gelwas dried for 2 days at 40° C. in a vacuum drying cabinet, milled togive a powder and the powder was annealed for 7 h at 450° C. in air.

0.86 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 0.7% palladium and 5% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 5. Analysis showed that after 1 h 10.2% diphenylcarbonate, after 2 h 16.8% diphenyl carbonate and after 3 h 21.3%diphenyl carbonate were present in the reaction mixture. 13.4 g of aphenol/water mixture had condensed in the cold trap.

Example 7

Preparing a Si/Mn co-gel and Coating with Palladium

5.2 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. 44 mlof a 25% strength aqueous ammonia solution were added to the mixturewith stirring. The mixture was covered loosely with paper and allowed tostand for 7 days at room temperature to gel. Then the gel was dried for3 days at 40° C. in a vacuum drying cabinet, milled to give a powder andthe powder was annealed for 6 h at 500° C. in air.

1.16 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel was added thereto and stirred for 1 h at 50° C. on aRotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 1.5% palladium and 3% manganese, each calculatedas the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 1, with the difference that 6.7 g of catalystwere used. Analysis showed that after 1 h 12.8% diphenyl carbonate,after 2 h 18.5% diphenyl carbonate and after 3 h 25.6% diphenylcarbonate were present in the reaction mixture. 15.6 g of a phenol/watermixture had condensed in the cold trap.

Example 8

Preparing a Si/Mn/Ce co-gel and Coating with Palladium

10.4 g of Mn(acac)₃ were dissolved in 200 ml of ethanol in apolypropylene beaker and mixed with 100 ml of tetraethoxysilane. Asolution of 0.12 g of cerium (III) acetate in 39 ml of 8N HCl was addedto the mixture with stirring over the course of 20 minutes. The mixturewas covered loosely with paper and allowed to stand for 8 days at roomtemperature to gel. Then the gel was dried for 2 days at 40° C. in avacuum drying cabinet, milled to give a powder and the powder wasannealed for 3 h at 300° C. in air.

1.16 g of Pd(acac)₂ were dissolved in 100 g of acetylacetone, the driedand powdered gel added thereto and stirred for 1 h at 50° C. on arotavapor. The solvent was then distilled off and the catalyst driedovernight at 110° C. under vacuum in a drying cabinet.

The catalyst contained 1.5% palladium, 0.2% cerium and 6% manganese,each calculated as the metal.

Use of the co-gel Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as in example 7. Analysis showed that after 1 h 9.1% diphenylcarbonate, after 2 h 15.8% diphenyl carbonate and after 3 h 23.1%diphenyl carbonate were present in the reaction mixture. 14.2 g of aphenol/water mixture had condensed in the cold trap.

What is claimed is:
 1. A Process for preparing an organic carbonatecomprising (A) obtaining a supported catalyst by a process comprising(i) preparing a gel containing at least one member selected from a firstgroup consisting of silicon oxide, aluminum oxide, titanium oxide andzirconium oxide and at least one member selected from a second groupconsisting of metal oxides of the elements of groups 4, 5, 6, 7, 11, 12,13, 14, the iron group (atomic numbers 26 to 28) and the rare-earthmetals (atomic numbers 58 to 71), and (ii) aging said gel to obtain anaged gel, (iii) drying said aged gel to obtain dry mixed metal oxides,(iv) shaping said dry mixed metal oxides to obtain a shaped mixed metaloxide and (v) applying at least one platinum metal component selectedfrom the group consisting of platinum metals (atomic numbers 44 to 46and 77 and 78) and compound of said platinum metals to said shaped metaloxide, in an amount 0.01 to 15 wt. %, calculated as platinum metal withrespect to the total weight of said supported catalyst, to obtain asupported catalyst and (B) reacting an aromatic hydroxy compound withcarbon monoxide and oxygen in the presence of said supported catalyst.